The invention relates to a transmission device delay monitoring method and device and a switch transmission delay monitoring system. The transmission device delay monitoring method comprises the stepsof receiving an SV (Sampling Value) message sent by a combination unit through a transmission device and recording the arrival time of the SV message; calculating the actual sampling moment of the sampling values in the SV message based on the arrival time and the SV message and calculating the time difference between the sampling moment and the last sampling moment; when the time difference is beyond the set time difference range, judging that the data transmission has delay jitter and obtaining the protection type of a relay protection device; and if the protection type belongs to an appointed protection type, marking that the sampling values are invalid and locking the corresponding protection function. According to the technical scheme, when the delay jitter results in protection malfunction of the relay protection device, the sampling values are marked to be invalid and the corresponding protection is locked to accordingly prevent the relay protection device against protection malfunction which is resulted from the transmission delay jitter and improve the protection triggering accuracy of the relay protection device.